1. Field of the Invention
This invention relates to an interchangeable finder device of a single lens reflex camera.
2. Description of the Prior Art
There has heretofore been proposed an automatic focus detecting interchangeable finder device of a single lens reflex camera which contains therein a focusing screen with a pentaprism, an eyepiece, etc. In this finder device, the positional relation among the pentaprism, the eyepiece, the focusing screen, etc. is fixed and therefore, the length of the optical path from the focusing screen to the eyepiece is always constant. This leads to an advantage that a predetermined visibility can always be obtained if the focusing screen can be fixed at a predetermined position when the finder device has been mounted to the camera body. Also, as regards a focus detecting optical system contained in this interchangeable finder device, the positional relation between the focus detecting optical system and the focusing screen is fixed and therefore, the distance from the focusing screen to a distance measuring light-receiving element is always constant. This leads to an advantage that no focus detection error will occur if the focusing screen can be fixed at a predetermined position when the finder device has been mounted to the camera body.
In such interchangeable finder device, however, the positional relation between the finder optical system including the focusing screen and the mounting-dismounting device is fixed and therefore, the positional relation between the focusing screen and the mounting-dismounting device must be predetermined so that the focusing screen lies at a predetermined position relative to the camera body when the finder device has been mounted to the camera body by means of the mounting-dismounting device. That is, high accuracy is required for making the positional relation between the focusing screen and the mounting-dismounting device into a predetermined positional relation.